Recently, as awareness of the environmental problems rises to a higher level, solar cells are in the spotlight as clean energy resources. Currently, solar-cell modules that are constituted in various types are developed and suggested. In general, a solar-cell module is constituted by laminating a transparent front substrate, a solar cell element, and a rear-surface protecting sheet through a sealing material sheet.
Ethylene-vinyl acetate copolymer resin (EVA) has been the most commonly used material as the sealing material sheet used for protecting a solar cell element filled in a solar-cell module from outside impact, and also for preventing the invasion of water into the solar-cell module. However, EVA resin tends to slowly decompose as it is used for a long period of time, and thus, deteriorates in the solar-cell module, thereby having the possibility of decreasing strength or generating acetic acid gas affecting the solar cell element. In order to solve such a problem, a sealing material sheet for a solar-cell module, which is formed by using a polyethylene-based resin instead of an EVA resin, has been suggested (see Patent Document 1).
In addition, for example, a sealing material sheet formed by a modified ethylene-based resin including alkoxysilane as a co-polymerization component is known as a polyethylene-based sealing material sheet. In addition, a sealing material sheet crosslinked by a modulation process or a subsequent heating process after combining such a modified ethylene-based resin with a crosslinking agent is known (see Patent Document 2). Such a polyethylene-based sealing material sheet has weatherability and durability that are equivalent to or more than that of a sealing material sheet of an EVA resin, and thus, may be preferably used as a sealing material sheet for a solar-cell module.
Meanwhile, a sealing material sheet for a solar-cell module requires high adhesion to other members that are laminated above and below in a solar-cell module. However, for the above-described polyethylene-based sealing material sheet, there is room for further improvement in consideration of adhesion to electrodes of a solar cell element constituted of zinc oxide, and the like, especially. As the thing that can solve such a problem, a sealing material sheet for a solar-cell module, which is formed by using the resin added with an ethylene copolymer including glycidyl methacrylate (GMA) as an adhesion improving agent, has been suggested (see Patent Document 3).
Patent Document 1: Japanese Unexamined Patent Application, Publication No. 2000-91611
Patent Document 2: Japanese Unexamined Patent Application, Publication No. 2009-10277
Patent Document 3: Japanese Unexamined Patent Application, Publication No. 2011-77358